Mobile communication base stations can be largely classified into an opened base station, a closed base station and a hybrid base station in a method for controlling an access to a mobile station. The opened type base station is a base station which provides all mobile stations with services regardless of the qualification of a mobile station. The closed type base station is a base station which organizes a closed subscriber group (CSG) consisting of specific mobile stations and offers services only to the mobile stations corresponding to CSG members.
Meanwhile, the hybrid base station is a base station which supports all of the opened and closed base stations. The hybrid base station operates in a closed type for the CSG members, and operates in an open type for general mobile stations which are not the CSG members.
Such user access control method has been introduced as the use of base stations for personal possession or private use increases in addition to the use of base stations for the existing enterpriser's possession or common use. In particular, as femtocell base stations that provide a mobile communication service in areas of approximately 100 m radius inside homes or buildings start to be installed, the user access control method became an essential element. On the other hand, hybrid cells stand for cells that are controlled by hybrid base stations, and serve as an important factor of supporting the enlargement of cell coverage and avoiding interferences between macro cells and femto cells. Meanwhile, a paging is to call and find a mobile station within a specific paging area in a mobile communication system. The paging area indicates an area that is discriminated by a unit of tracking of mobile station, and is defined as a location area (LA) or tracking area (TA) in 3rd generation partnership project (3GPP). A paging optimization is a method which minimizes unnecessary calls of the mobile station through a paging. Since the paging requires using radio resources such as a paging channel, the paging optimization provides an effect of enhancing the performance of system by reducing the use of unnecessary radio resources. Particularly, when a number of femtocell base stations are designated as one paging area, the reduction of unnecessary paging is effective in the reduction of signaling between a core network and the base stations.
A conventional method for paging optimization involves removing unnecessary paging in a closed cell environment. For instance, when a mobile station as a paging target is subscribed to a CSG, a core network obtains an allowed CSG list of the mobile station as the paging target before performing a paging to a paging area. The allowed CSG list of the mobile station is a set of CSG identifiers (IDs) of base stations that mobile stations as CSG members can receive mobile communication services. Among base stations belonging to the paging area, the CSG IDs of base stations operating in a closed type are checked to exclude base stations that do not exist in the allowed CSG list of the mobile station from paging targets. That is, for closed base stations to which a mobile station cannot access among base stations as the paging targets, no paging is attempted.
Meanwhile, in the conventional method described above, base stations operating in an open or hybrid type have been excluded from paging optimization targets. This is because the opened or hybrid base stations can provide services for general users or non-allowed CSG members due to its nature. Thus, in the conventional paging optimization method, all of base stations operating in an open or hybrid type are included in the paging targets.
FIG. 1 shows a conventional radio communication system. Mobile communication base stations can be classified into an opened base station, a closed base station, and a hybrid base station in a method for controlling an access to a mobile station. In FIG. 1, a first base station 130 operates as an opened base station, and second and third base stations 140 and 150 operate as closed base stations. And, fourth and fifth base stations 160 and 170 operate as hybrid base stations. The first to fifth base stations are connected to a core network device 100 via an IP network 120.
The conventional paging optimization method excluded only closed base stations to which a mobile station cannot access from the paging targets. In the conventional method, since the base stations that operate in the open or hybrid type can be used by general users or mobile stations that are not the CSG members, all of these base stations are included in the paging targets without checking the optimization conditions upon paging.
Referring to FIG. 1, the second and third base stations 140 and 150 which are the closed base stations may be included in the paging optimization targets and thus may not be the paging targets, but the first base station 130 which is the opened base station and the fourth and fifth base stations 160 and 170 which are the hybrid base stations are necessarily included in the paging targets. However, the present invention allows the hybrid base stations not to belong to the paging targets by also including them in the paging optimization targets.
In other words, the conventional method has a limit in the efficiency because the base stations that are the paging optimization targets are limited to closed base stations only.
Consequently, there is an increasing need for a hybrid base station because of the enlargement of coverage area, interference avoidance and the like. However, the present invention allows the hybrid base stations not to belong to the paging targets by also including them in the paging optimization targets.